Raddrizzatori ad alto fattore di potenza bidirezionali avanzati per microreti in cc

This dissertation focuses on the development of PFC converter topologies aimed at enhancing the interlinking between ac grids and dc microgrids. The primary objective is to propose novel converter topologies that enable a more efficient, compact, flexible, and reliable interface between ac and dc systems. The research activities begin with a comparative evaluation of bidirectional single-stage non-isolated buck-type topologies. The evaluation criteria include the number of semiconductors, semiconductor stresses and losses, magnetic component sizes and losses, and heat sink size. This evaluation is conducted using an analytical power loss model and PLECS simulations. The results indicate that the Y-converter offers superior overall performance compared to the other topologies, making it a promising candidate for this application. A 10-kW prototype of the Y-converter is then constructed, demonstrating a peak efficiency of 99.26% and an efficiency of 97.47% at rated output power. Building on the motivations for the Y-converter, a modified three-phase four-wire bidirectional topology, named the Four-wire Y-converter, is proposed. This configuration incorporates the ac grid’s neutral by directly connecting it to the positive terminal of the dc microgrid. The inclusion of the neutral wire enables islanded operation of the hybrid microgrid, ensuring a stable power supply for both single-phase and three-phase ac loads. Additionally, the direct connection between the ac microgrid neutral and the dc microgrid’s positive terminal allows for grounding of both microgrids, a feature previously achievable only with isolated topologies. The Four-wire Y-converter also demonstrates control over positive, negative, and zero sequence components, providing flexibility under ac voltage imbalances to ensure optimal performance. Furthermore, the converter allows for independent phase control, enabling fault-tolerant operation, which is validated under single-phase fault conditions. The converter’s performance is thoroughly assessed through experimental testing on a 7-kW prototype under various conditions, including balanced and unbalanced ac voltages, single-module disconnection, and islanded operation. The scope of the research transitions from two-port converters to multiport converters, driven by the rising popularity of dc systems and the corresponding demand for advanced power converters. A single-stage non-isolated multiport converter, named the Multiport Y-converter, is proposed to interface the three-phase ac grid with dc systems. The key motivations for the Multiport Y-converter include its single-stage power conversion across multiple ports, which improves efficiency and power density. The absence of bulky intermediate dc-link capacitors and transformers further reduces cost and size. Additionally, the converter features buck-boost capability and bidirectional power flow at all ports, independent of the dc ports' voltage levels, providing flexibility to interface with a wide range of dc systems. Lastly, another single-stage non-isolated multiport converter, named the Asymmetric Multiport Y-converter, is proposed to interface the three-phase ac grid with dc systems. The Asymmetric Multiport Y-converter features a more compact structure compared to the Multiport Y-converter, potentially leading to a lower-cost power converter, particularly when interfacing two dc ports with differing power levels. Challenges inherent to the Asymmetric Multiport Y-converter, such as maintaining balanced ac grid currents due to its asymmetric design and minimizing low-frequency voltage ripples at the dc ports, are addressed with proposed solutions. The multiport converters’ performance is validated through experimental tests under various operating conditions, including steady-state and transient results, as well as efficiency evaluations.